The documentation should show an example of typical correct usage

While it might seem obvious to people familiar with this crate, I am actually confused how to use this crate after just landing on it looking for a constant comparison crate. What I want to do is: ``` if password_in_request != password_in_the_config { bail!("Wrong password"); } ``` for usual reasons. I open https://docs.rs/subtle/ , I can see `ConstantTimeEq` and it is clear I should use `ct_eq`. But then ... why is it returning `Choice`? Am I supposed to call `.into()` on it? It seems so... ? But why can't `ct_eq` return `bool` right away by doing that `.into()` under the hood? Unclear. So, it seems to me that the documentation can be improved in two ways: * Please add an idiomatic example on a front page of a correct usage. It will take one short paragraph and give an immediate answer to developers that are just looking for a solution. * Please somewhere early in the documentation of `Choice` explain *why*: Why does it exist, why can't `ct_eq` just return `bool`.